As demands for achievement of energy saving and cost saving are accelerated in recent years, saving the amount of water used in a variety of water based systems such as washing water systems, water systems associated with membrane process, and water systems associated with reinjection well of geothermal power plant has been expected. Therefore, techniques for reducing the amount of water blown out from the system, and operating under a highly concentrated condition were developed.
As a result of operation at high concentrations in such water systems, concentrations of silicic acid salts as well as metal salts of calcium, magnesium etc., in water increase, whereby deposition occurs by scaling on the metal surface, particularly the heat transfer surface or the like, that is in contact with water, leading to: a problem of expansion, curling, rupture and the like due to superheating of the steel material of the heat transfer surface, caused by deterioration of heat transfer efficiency; and a problem of occlusion of flow channel of water due to growth of the scale and scale pieces generated by detachment, and the like.
In order to solve these problems, it is necessary to add to the water system a water-treating agent having an action of inhibiting the deposition of scale, thereby inhibiting the adhesion of scale components into the system, and to discharge the components out of the water system by blowing.
Conventionally, as the water-treating agent for preventing silica-based scale, those containing various hydrophilic polymers such as polyacrylamide (Patent Document 1), polyethylene glycol (Patent Document 2), polyvinylformamide (Patent Document 3), terpolymers of acrylic acid, acrylamidemethylpropanesulfonic acid and N-substituted acrylamide (Patent Document 4), and polyvinylpyrrolidone (Patent Document 5) were proposed.
[Patent Document 1] Japanese Unexamined Patent Application, Publication No. S61-107998
[Patent Document 2] Japanese Unexamined Patent Application, Publication No. H02-031894
[Patent Document 3] Japanese Unexamined Patent Application, Publication No. H10-323696
[Patent Document 4] Japanese Unexamined Patent Application, Publication No. H04-356580
[Patent Document 5] Japanese Unexamined Patent Application, Publication No. H11-057783